Historically, the pneumatic tire has been fabricated as a laminate structure of generally toroidal shape having beads, a tread, belt reinforcement, and a carcass. The tire is made of rubber, fabric, and steel. The manufacturing technologies employed for the most part involved assembling the many tire components from flat strips or sheets of material. Each component is placed on a building drum and cut to length such that the ends of the component meet or overlap creating a splice.
In the first stage of assembly the prior art carcass will normally include one or more plies, and a pair of sidewalls, a pair of apexes, an innerliner (for a tubeless tire), a pair of chafers and perhaps a pair of gum shoulder strips. Annular bead cores can be added during this first stage of tire building and the plies can be turned around the bead cores to form the ply turnups. Additional components may be used or even replace some of those mentioned above.
This intermediate article of manufacture would be cylindrically formed at this point in the first stage of assembly. The cylindrical carcass is then expanded into a toroidal shape after completion of the first stage of tire building. Reinforcing belts and the tread are added to this intermediate article during a second stage of tire manufacture, which can occur using the same building drum or work station.
This form of manufacturing a tire from flat components that are then formed toroidally limits the ability of the tire to be produced in a most uniform fashion. As a result, an improved method and apparatus has been proposed, the method involving applying an elastomeric layer on a toroidal surface and placing and stitching one or more cords in continuous lengths onto the elastomeric layer in predetermined cord paths. The method further includes dispensing the one or more cords from spools and guiding the cord in a predetermined path as the cord is being dispensed. Preferably, each cord, pre-coated with rubber or not so coated, is held against the elastomeric layer after the cord is placed and stitched and then indexing the cord path to a next circumferential location forming a loop end by reversing the direction of the cord and releasing the held cord after the loop end is formed and the cord path direction is reversed. Preferably, the indexing of the toroidal surface establishes the cord pitch uniformly in discrete angular spacing at specific diameters.
The above method is performed using an apparatus for forming an annular toroidally shaped cord reinforced ply which has a toroidal mandrel, a cord dispenser, a device to guide the dispensed cords along predetermined paths, a device to place an elastomeric layer on the toroidal mandrel, a device to stitch the cords onto the elastomeric layer, and a device to hold the cords while loop ends are formed. The device to stitch the cords onto the elastomeric layer includes a bi-directional tooling head mounted to a tooling arm. A pair of roller members is mounted side by side at a remote end of the tooling head and defining a cord exiting opening therebetween. The arm moves the head across the curvature of a tire carcass built on a drum or core while the cord is fed through the exit opening between the rollers. The rollers stitch the cord against the annular surface as the cord is laid back and forth across the surface, the first roller engaging the cord along a first directional path and the second roller engaging the cord in a reversed opposite second directional path.
The toroidal mandrel is preferably rotatable about its axis and a means for rotating is provided which permits the mandrel to index circumferentially as the cord is placed in a predetermined cord path. The guide device preferably includes a multi axis robotic computer controlled system and a ply mechanism to permit the cord path to follow the contour of the mandrel including the concave and convex profiles.
While working well, certain challenges exist in the aforementioned proposed apparatus and method. First, it would be desirable to maintain a more constant optimal tension in the cord that is being applied to the toroidal core surface. In order to achieve proper placement of the cord onto an underlying layer, a constant optimal tension must be maintained in the cord as it is fed through the tooling head and applied to the toroidal core surface. Excessive tension can damage or break the cord or cause a tooling head malfunction as it lays the cord upon the underlying layer. Excessive tension in the cord that causes breakage requires time-consuming re-routing of the cord through the applicator head, resulting in an undesirable and costly delay in the manufacture of the tire. On the other hand, too little tension in the cord may result in cord misalignment through the applicator head and a less than optimal positioning of the cord on the underlying layer. Improperly placed cord on the annular substrate can result in wasteful scrapping of work in process.
Existing cord tensioning mechanisms in tooling heads generally rely on a systemic tensioning of the cord between the applicator rollers and the spool from which the cord is drawn to maintain the cord in a proper state of tension. Such a reliance has, however, proven to be misfounded. It is inherently difficult to maintain a proper level of cord tension between a feed spool and an end of arm tooling roller due to variations in the spacing between the roller and spool as the roller rides over an annular substrate that may include surface anomalies and varying thickness. Consequently, as the roller in an existing applicator head moves over a surface having such anomalies, the cord is placed into greater or lesser tension than desirable.
A need, accordingly, remains for a cord tensioning and feed mechanism for an applicator head that is simple to construct, operationally reliable and efficient, and effective in maintaining an optimal level of tension within a cord stream that is fed through an applicator head to an annular substrate. Furthermore, a need exists for a cord tensioning and feed mechanism that can adjusts the tension within the cord as close as possible to the applicator head so as to minimize the chance for the tension to change as the cord is fed through the applicator head to the annular substrate.